Traditional breeding falls short in boosting soybean photosynthesis

A team from the University of Illinois has determined that improving a key component of soybean photosynthesis is unlikely to come from traditional breeding methods, and that gene editing is likely the key to unlocking soybean potential.

“There’s not a huge amount of room to improve the light-harvesting efficiency of soybean photosynthesis at a cellular level using what’s available naturally from traditional breeding,” said Steven Burgess, assistant professor in plant biology at Illinois. “If people are going to pursue this strategy, it really needs to be either gene editing or transgenic approaches.”

While photosynthesis, the natural process all plants use to convert sunlight into energy and yields, has been at the basis of plant life for millions of years, it is not optimized for current agricultural systems. This is because wild species don’t evolve to maximize yield and typically encounter a range of environmental challenges like pest or nutrient limitations that are alleviated by modern agronomic practices. Photoprotection, which Burgess described as “the ability of plants to safely dispose of excess energy,” is particularly inefficient. When a plant’s leaves absorb too much sun, often because of extended exposure on sunny days, that excess energy can hurt the plant’s growth potential if it’s not disposed of correctly, or if there’s just too much energy produced.

“Photoprotection is essential to prevent plants from suffering damage under strong light, however, when plants become shaded, either from clouds or other leaves, they are often slow to turn it off. This means they lose potential energy that could be used for growth,” said Burgess. “Previous computational modeling and transgenic studies had suggested it is possible to speed up this process, increasing the overall energy available for the plant. We wanted to see if we could confirm those predictions”

This work was conducted as part of Realizing Increased Photosynthetic Efficiency (RIPE), an international research project that aims to increase global food production by developing food crops that turn the sun’s energy into food more efficiently. RIPE was supported from 2017-2023 by the Gates Foundation, Foundation for Food & Agriculture Research, and U.K. Foreign, Commonwealth & Development Office and is currently supported by Gates Agricultural Innovations (Gates Ag One).

Burgess and his team planted, collected, and analyzed field trials for three years, observing the entire developmental stage of different soybean varieties to better understand how things worked and what changed throughout the growing season. Their work was recently published in The Plant Journal.

“No one had looked at how much variation there is [in relaxation of photoprotection] for traditional soybean breeding before,” said Burgess, a former principal investigator for the RIPE project. “Additionally, most of the measurements taken on other species were generally done under controlled conditions, rather than in the field, which is crucial because of the huge impact the environment has on photosynthesis.”

The role of the environment is why the team’s detailed measurements throughout an entire growing season were so important. They gathered data about the total amount and rate of photoprotection relaxation at six time points across various points of plant development, along with crucial environmental data such as precipitation, temperature, hours of sunlight, and evaporation potential. Seeing how different soybean genotypes compared in a variety of times and conditions gave the scientists the best overall picture of how these genetics would perform in other fields and environments.